Carbon materials can impart electric conductivity, thermal conductivity and the like on resin materials, coating materials and the like. Moreover, carbon materials are also used as an electrode material for a battery. For these carbon materials, known are carbon nanofibers, carbon nanotubes, carbon black and the like.
Carbon nanofibers have a relatively thick fiber diameter of 50 nm to 300 nm, and a fiber length of about 10 μm (FIG. 1). Such carbon nanofibers show weak entanglement between the fibers, and thus each of the carbon nanofibers can be easily dispersed by adding to a matrix and kneading. However, when trying to sufficiently construct electrically conductive networks by connecting the carbon nanofibers to each other, a large amount of the carbon nanofibers needs to be added.
On the other hand, carbon nanotubes have a thin fiber diameter of 5 nm to 40 nm and a fiber length of 3 μm to 10 μm, showing an aspect ratio of near 1000 (FIG. 2). Such carbon nanotubes show entanglement between the fibers to form aggregates of several hundred micrometers (FIG. 3). When the aggregates of such strongly entangled carbon nanotubes is added to a matrix and kneaded, the aggregates only become finer, and the structure of the aggregates still remains. Therefore, it is difficult to achieve a state in which each of the carbon nanotubes is untangled. As a result, an electric conductivity imparting effect may not be as good as expected.
Further, carbon blacks represent particles having a primary particle diameter of several nanometers to several tens of nanometers. The carbon blacks form a secondary structure called “STRUCTURE” in which primary particles are lined up. This STRUCTURE usually has a line-up length of as short as about 100 nm. The STRUCTURES can be relatively easily dispersed because they are not firmly aggregated.